<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<style>
    body{
        width: 1400px;
        overflow: hidden;
    }
    .box1{
        width: 400px;
        height: 300px;
        background-color: rebeccapurple;
        float: left;
    }

    .box2{
        width: 400px;
        height: 300px;
        background-color: mediumvioletred;
        float: left;
    }
    .box3{
        position: relative;
        width: 400px;
        height: 400px;
        background-color: royalblue;
        z-index: 22;
        top: 310px;
    }
</style>
<body>
<div class="box1">

</div>
<div class="box2"></div>
<div class="box3"></div>
</body>
</html>